1. Field of the Invention
The invention relates to deflected continuous ink-jet printing machines and, more particularly in such machines, it relates to a printing head or module that gives several simultaneous jets and allows an assembly of several adjacent printing modules having a constant pitch between jets in order to obtain a wide-format printing machine.
2. Description of the Prior Art
Deflected continuous ink jet printing heads are known, and one of them has been described in the co-pending U.S. patent application No. 07/687,925 entitled "Ink Jet Printing Head" corresponding to the published PCT application no. WO 91/05663. In the above-mentioned patent application, the head comprises the following in a single pack: at least two modulation elements comprising injection nozzles fed by a single ink circuit and a module for the recovery of unused drops, common to all the jets, with only one recovery outlet. The single pack has a base used as a support for the modulation elements, charge electrodes, phase detection or speed detection electrodes, and deflection electrodes, these different elements having to be aligned with a precision of the order of one-hundredth of a millimeter.
Such precision is very difficult to obtain when these elements are manufactured separately and then mounted on the base, and the greater the number of ink jets of the printing head, the more difficult it is to obtain this precision. Moreover, the number of adjustments to be made, notably adjustments of alignment, during the mounting and maintenance is high.
Besides, it can be seen that a printing head of this type is ill-suited for the design of a row of several tens of ink jets as the cost of manufacturing and maintaining such a system would be very high.